Method and apparatus for spotter beam formation using a partitioned optical element

ABSTRACT

An optical element for causing a visible spotter beam emitted by a hand-held scanning bar code reader provides visible indications of the area of a surface which is being scanned by an invisible scanning beam. The optical element transforms the visible spotter beam, at its extreme of travel, into two pairs of cursor beams which are directed along predetermined trajectories relative to the trajectory followed by the scanning beam. The predetermined trajectories can be above and below, or to the left and right of the center of travel of the invisible scanning beam. In one embodiment, a method of identifying the proper focusing distance of the scanning reader is presented. The method identifies the focusing distance by making the pairs of cursor beams formed from the visible beam at its two angular extreme of travel to form a predetermined pattern indicating the proper focusing distance. The optical element can be made from segmented or gradient surfaces, such as Fresnel surfaces, or from a holographic optical element.

TECHNICAL FIELD

This invention relates to the formation of a spotter beam on a targetobject and, more particularly, to spotter beam formation in conjunctionwith a bar code reader.

BACKGROUND OF THE INVENTION

A bar code reader typically uses a beam of light to read a bar code,which consists of alternating bars of differing reflectivities. Thescanner then receives and interprets the fluctuations in the returninglight that are caused by the bar code. It is known in the prior art toread bar codes by means of a hand-held wand which makes contact with thesurface on which the bar code is printed. However, the need to makecontact with the surface is frequently inconvenient and givesuninterpretable readings because the wand is not moved across the barcode with a sufficiently uniform velocity.

An alternative to a wand is a hand-held scanning reader which does notrequire physical contact with the bar code being read. A scanning readertypically produces a beam of light, called a scanning beam, which isscanned repetitively across a target object. If the scanning beamintercepts a bar code (or some other symbology), portions of it will bereflected back toward the scanning reader in a pattern corresponding tothe pattern of the symbology encountered. This modulated light isdetected by sensing circuitry in the scanning reader which in turnproduces an electrical signal related to the returning light. Theelectrical signal is then analyzed to provide an indication of therelative widths of the bars and spaces of the bar code on the basis ofrelative time. That is, the widths of the alternating areas of differentreflectivity are determined on the basis of the relative time durationof corresponding portions of the electrical signal, as related to thetime for a single scan, also called the scanning time. This allows thescanning reader to be used with bar codes which have a wide variety ofsizes, the important factor being that the relative widths of theelements of the bar codes be preserved. Accordingly, it is prferablethat the scanning beam be scanned across the bar code at a substantiallyuniform rate in order to ease the task of interpreting the bar code.

In order to insure that the scanning beam is scanned at a substantiallyuniform rate, the scanning beam is typically reflected from a mirrorwithin the scanning reader that moves in a repetitive pattern at auniform rate. The mirror is generally driven by a small electrical motorunder the control of electronic control circuitry. The mirror istypically either rotating at a constant speed or oscillating on the endof a shaft attached to a motor which can step between two extremeangular positions. Examples of rotating optical elements are shown inU.S. Pat. Nos. 4,025,761; 4,097,729; 4,450,350; 4,575,625; and4,692,603. Examples of oscillating mirrors, also called ditheringmirrors, are shown in U.S. Pat. Nos. 4,593,186; 4,736,095; and4,808,804. In hand-held applications, a dithering mirror is generallypreferable, since it can be made both lighter and more compactly than arotating optical element.

The light source in a modem bar code scanner is generally a very lowpower solid state laser diode, since such devices are efficient andlight, and can be made reliably and relatively inexpensively. Suchdevices may emit visible or invisible light. Where the light is visible,the scanning beam produces a visible line on the target object whichhelps the user to align the reader to a target object.

In many applications, the laser light is not visible to an operator.Thus, the operator is not able to determine if a beam of laser light isbeing emitted. Additionally, the user does not have any guide by whichto align or focus the laser light. It is helpful to provide a visuallydiscernible guide to indicate the existence and direction of the laserlight to permit a user to "target" or "spot" the beam of laser light ona target object. Such beams are referred to as spotter beams.

It is known in the art to produce a spotter beam to aid the alignment ofan invisible scanning beam with a target object. The spotter beamtypically is a visible light beam directed toward the target objectwhich presents a visible image near to, or superimposed upon, thescanning beam. The position of the visible image indicates to anoperator the location of the invisible scanning beam's contact with thetarget object. The light source used for a spotter beam is typically acommercially available light-emitting diode (LED).

One known method of producing a spotter beam alternates the emission ofthe laser light with the visible light. This requires careful control ofthe timing of the laser diode and visible light LED so that the laserlight is terminated during a short period of time during which thevisible light LED is activated. In systems employing this method, thevisible light emission is directed optically along the same scan path asthe laser light. A collinear, visible light image and the invisiblescanning beam are alternately shown on the target objects. Readersemploying either of the above (i.e., visible scanning beam or invisiblescanning beam combined with a visible spotter beam) typically produce asingle, linear visible image for the user's reference. They do notprovide any substantial indication of an appropriate focusing distanceor parallel alignment of the scanning reader to the target object.

Another problem with such readers is that the dithering mirror stops ateach angular extreme and returns over the same segment, causing thevisible light from either the scanning beam or the spotter beam to dwellat the end of its travel and produce an undesirable bright spot at eachend of the visible image.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an optical systemfor providing an improved alignment beam.

It is a further object of the present invention to provide an alignmentbeam that indicates when a scanning beam is properly focused on a targetsurface that may bear a symbology.

These and other objects can be provided by an apparatus for forming avisible scanning beam of light directed toward a target object. Theapparatus comprises a source of a beam of visible light, and a scanningapparatus receiving the beam of visible light and causing it to scanover a predetermined scan path along an optical axis forming a visiblescanning beam. The apparatus further comprises an optical elementreceiving the scanning beam and forming it into cursor beams when thescanning beam is located in predetermined portions of the predeterminedscan path and causes the spotter beam to be transmitted substantiallyunaffected in all other portions of the predetermined scan path.

In another aspect, the invention comprises an apparatus for focusing ascanning beam on a surface of a target object. The apparatus comprises asource of a beam of visible light, and a scanning apparatus receivingthe beam of visible light and causing it to scan over a predeterminedscan path to define a scanning beam. The apparatus further comprises anoptical element receiving the scanning beam that forms the scanning beaminto a pair of cursor beams when the scanning beam is located inpredetermined portions of the predetermined scan path, thus forming apredetermined pattern of cursor images on the target object when thereader is positioned such that the scanning beam is focused on thetarget object.

In another aspect, the invention is an apparatus for focusing aninvisible scanning beam on a surface of a target object. The apparatuscomprises a source of a beam of invisible light and a source of a beamof visible light, and a scanning apparatus receiving the beam ofinvisible light and the beam of visible light and causing them to scanover a predetermined scan path to define a spotter beam. The apparatusfurther comprises an optical element receiving the spotter beam thatforms the spotter beam into a pair of cursor beams when the spotter beamis located in predetermined portions of the predetermined scan path,thus forming a predetermined pattern of cursor images on the targetobject when the scanning beam is focused on the target object.

In a further aspect, the invention is a method for forming a visiblespotter beam of light on a target object. The method comprises the stepsof (a) forming a beam of visible light; (b) causing the beam of visiblelight to scan over a predetermined scan path to define a scanning beam;and (c) intercepting the scanning beam with an optical element; and(d)causing the scanning beam to be transmitted substantially unaffectedwhen the scanning beam is located in a first portion of the opticalelement and causing the scanning beam to form a cursor in a secondportion of the optical element.

In a still further aspect, the invention is a method for focusing aninvisible beam of light on a target object. The method comprises thesteps of (a) forming a beam of visible light; (b) causing the beam ofvisible light to scan over the predetermined scan path to form a spotterbeam; (c) receiving the spotter beam with an optical element; (d)causing the spotter beam to be transmitted in a portion of the opticalelement; (e)causing the spotter beam to be formed into a first cursorbeam, directed in a first direction when the spotter beam is in ascanned portion of the optical element; (f) causing the spotter beam tobe formed into a second cursor beam directed in a second direction whenthe spotter beam is in a third portion of the optical element; (g)directing the cursor beams onto a target object to form a pair of cursorimages; and (h)adjusting the positions of the cursor images to produce adesired pattern of cursor images on the target object by adjusting thedistance between the optical element and the target object.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a hand-held scanning laser bar codereader.

FIG. 2 is a top plan view of the scanning laser bar code reader of FIG.1.

FIG. 3 is an enlarged perspective view of a portion of optics of thescanning laser bar code reader of FIG. 1 shown removed from its case.

FIG. 4 is a schematic diagram of the circuitry of the motor driveelectronics of the scanning laser bar code reader shown in FIG. 1.

FIG. 5 is an enlarged top view of a portion of the optics of analternative embodiment of the scanning laser bar code reader of FIG. 1including optical elements for producing a spotter beam shown removedfrom its case.

FIG. 6A is an enlarged plan view of a first embodiment of the opticalelement of the scanning laser bar code reader of FIG. 1.

FIG. 6B is a cross-sectional view taken substantially along line 6A-6Bof FIG. 6A.

FIG. 7A is an enlarged plan view of a second embodiment of the opticalelement of the scanning laser bar code reader of FIG. 1.

FIG. 7B is a cross-sectional view taken substantially along line 6A-6Bof FIG. 7A.

FIG. 8 is a schematic drawing of a portion of the visible beams formedby the scanning laser bar code reader of FIG. 1.

FIG. 9 is a schematic drawing of cursor images produced by the scanninglaser bar code reader of FIG. 1 with the optical element of FIGS. 6A and6B demonstrating use for determining a focusing position of the bar codereader.

FIG. 10 is a schematic drawing illustrating focusing using the scanninglaser bar code reader of FIG. 1.

FIG. 11A is a plan view of a third embodiment of the optical element ofthe scanning laser bar code reader of FIG. 1.

FIG. 11B is a cross-sectional view taken substantially along lines11A-11B of FIG. 11A.

FIG. 12 is a schematic drawing of a portion of the visible beams formedby the third embodiment of the optical element of FIGS. 11A and 11B.

FIG. 13 is a schematic drawing of cursor images produced by the scanninglaser bar code reader of FIG. 1 with the optical elements of FIGS. 11Aand 11B demonstrating use for determining a focusing position of the barcode reader.

DETAILED DESCRIPTION OF THE INVENTION

A hand-held scanning laser bar code reader 10 incorporating the presentinvention is shown in FIGS. 1 and 2. The scanning reader 10 includeselectronic circuitry and optical components contained within a case 12.It also includes a keyboard 14 and liquid crystal display (LCD) 16 forthe exchange of information with a user, such as data read from a barcode or feedback for programming the scanning reader 10.

Upon actuating a pair of opposed triggers 18 (only one being shown inFIG. 1), the scanning reader 10 is activated, and, as will be describedsubsequently, produces a scanning beam of laser light. The scanning beampasses through a window 20 placed in a top end 21 of the scanning reader10, as shown in FIG. 2. The scanning occurs in a scanning plane 24 alongthe directions shown in FIG. 2 by a pair of arrows. The scanning beam isprojected outwardly from the scanning reader 10 within the scanningplane 24. If the scanning beam reaches a surface, some of the opticalenergy of the scanning beam impinging on the surface is reflected andreturns to the scanner through the window 20 where it can be detected ina conventional manner. If the reflecting surface upon which the scanningbeam impinges contains a symbology, such as a bar code, the opticalenergy returning to the scanning reader 10 will be modulated by thepattern of reflectivities which the bar code symbology contains. Themodulated optical energy received by the scanning reader 10 upondetection produces an electrical signal which can be amplified andprocessed by circuitry in accordance with techniques which areconventional to those skilled in the art of bar code reader design.

With reference to FIG. 3, the wavelength of the scanning beam producedwithin the scanning reader 10 is determined by a laser diode 32 which iscontained in the scanning reader 10. The laser diode 32 preferablyproduces human-visible light.

The laser diode 32 is mounted within the reader 10 and is supplied withelectrical power through electrical leads 40 by conventional electroniccircuitry contained elsewhere in the scanning reader 10. Associated withthe laser diode 32 is a holder 42 which contains and holds, as a fixedassembly, lenses and other optical elements which are required to shapethe scanning beam into the desired form. The scanning beam is generatedfrom a beam of laser light produced by the laser diode 32 by passing thebeam of laser light from the laser diode 32 through one or more lenses31 to aid in focusing the beam of laser light at a particular distanceexterior to the scanning reader 10 and through an aperture stop 33 toreshape the beam to have a desired cross-section.

After the beam of laser light passes through the optical elementssupported by the holder 42, it passes through a hole 44 in the turningmirror 34. The beam of laser light then travels to the dithering mirror36. The dithering mirror 36 is attached to the motor 38 by a shaft 46,which causes the dithering mirror 36 to oscillate or "dither" about anaxis aligned with the shaft 46 in a conventional manner.

The scanning plane 24 (see FIG. 2) is perpendicular to the axis alignedwith the shaft 46. The beam of laser light reflects from the ditheringmirror 36 and is directed through a predetermined scan path to form thescanning beam. The scanning beam then passes through the window 20 at aposition within the scanning plane 24, depending on the angular positionof the dithering mirror 36.

With reference to FIG. 5, the alternative embodiment of the reader issubstantially similar to the reader of FIG. 3, with the addition ofcomponents for producing visible spotter beam and the use of a laserdiode 32 emitting only invisible light (i.e., light which is beyond thewavelength of human vision). The additional components include an LED 50and a dichroic mirror 52. The LED 50 is chosen so that the light itemits is at a wavelength that is visible to the human eye. The LED 50 iscontained within a housing 54 that shapes the light emitted onto anarrow beam, suitable for defining a very narrow spot on a surface ontowhich it is be projected. The LED 50 emits light toward the dichroicmirror 52 which reflects the light from the LED 50 toward the turningmirror 34. Note that the dichroic mirror 52, because it is dichroic,transmits light at the wavelength of the laser diode 32 while reflectinglight at the wavelength of the LED. The turning mirror 34 reflects thelight from the LED 50 toward the dithering mirror 36. From this pointon, the light from the LED 50 follows substantially the same path aslight from the laser diode 32, providing a visual indication to a userof the position of the light of the laser diode 32. This visible beam isreferred to herein as a spotter beam.

In the embodiments of FIGS. 3 and 5, any optical energy that is receiveddue to reflections from a target, such as one having a bar codesymbology, is transmitted through the window 20. The returning opticalenergy is reflected by the dithering mirror 36 onto the turning mirror34 to the photodiode 60 through the filter 62 and in the case of theembodiment of FIG. 5, through the dichroic mirror 52. The photodiode 60is aligned so that it receives essentially all of the received lightenergy transmitted through the filter 62. This maximizes the strength ofthe signal produced by the photodiode 60, thereby improving theperformance of the electronic circuitry which processes the signalsproduced by the photodiode 60.

As can be seen from the above discussion, the angular ranges of travelof the scanning beam and the spotter beam in the embodiment of FIG. 4are controlled largely by the dithering mirror 36, driven by the motor38. The motor 38 is a stepper motor having the capability of producingsteps which are eighteen degrees wide. As shown in FIG. 4, the motor 38includes two windings 80A and 80B. Each of the windings 80A and 80B iscenter-tapped, dividing the winding into two legs. The center of each ofthe windings is held at a substantially fixed first voltage, such as thesupply voltage for the electronic circuit of the scanning reader 10.Typically, the supply voltage is five volts. Each of the legs of the twowindings 80A and 80B can be excited separately. To accomplish this, theend of each of the legs is capable of being grounded (or held at someother voltage, if appropriate), respectively, through a circuitincluding one of the four transistors 82₁, 82₂, 82₃, 82₄. For example,if an appropriate signal is applied at line A, the gate of thetransistor 82₁ will cause current to pass through the upper leg of thewinding 80A. This will cause the motor 38 to rotate slightly. If signalsare applied to lines A, A, B, and B in the correct order, the motor 38,and consequently, the dithering mirror 36, can be caused to oscillate.This, in turn, will cause the scanning beam to be scanned through thewindow 20, as described above. If the signals are applied properly tothe lines A, A, B, and B, the scanning beam can be caused to move insuccessive passes through along the predetermined scan path having twoangular extremes, producing the scanning beam. If desired, the motion ofthe scanning beam between the two angular extremes can be made to have asubstantially constant angular velocity.

By selectively energizing the windings 80A and 80B, the dithering mirror36 can be rotated, sweeping the scanning beam through its full angularrange of travel. The angular range of travel occurs between twopredetermined angular extremes. By repetitively energizing the windings,the dithering mirror 36 can be caused to scan the beam repeatedlythrough this angular range of travel. For example, if it is desired tocause the dithering mirror 36 to scan the scanning beam and the spotterbeam forty times per second, a square wave train at a rate ofapproximately 800 Hz can be used to drive the stepper motor windings.

When no sweep is desired, the dithering mirror 36 is kept at one end ofits angular range of travel. The dithering mirror 36 is kept in place byactivating the lower legs of the two windings 80A and 80B, while the twoupper legs are not activated.

At the end of each scan, the dithering mirror 36 stops and reverses itsdirection of travel so as to return through the angular range of travelto its original position. The scanning beam thus passes through a regionat the angular extreme of the scan, stops, and quickly passes backthrough the same region. In prior art scanning systems, this resulted ina perceived bright spot at each end of a scan. To prevent this brightspot, it is known to inhibit the scanning beam during the time it is inthe region at the end of the scan. This can be done by switching off thevisible light source or by blocking the optical path of the scanningbeam when the dithering mirror 36 is near its angular extremes.

Rather than inhibit the bright spot, the present invention utilizes itas an aid to focusing and alignment by using it to form a visible"cursor image" for a user. The cursor image is typically brighter thanthe scanning beam making it relatively easily locatable and identifiableby a user as compared with the scanning beam. The cursor image isproduced using an optical element 20A shown in FIGS. 6A and 6B which isincorporated into the window 20. The optical element 20A includes afirst and second end portions 122, 124 with a central portion 120therebetween.

The optical element 20A intercepts the visible light produced by thelaser diode 32 and formed into the scanning beam as described above, andredirects the visible light depending upon which portion of the opticalelement 20A the scanning beam strikes. The central portion 120 isessentially flat having an upper surface 119 with a flatness of lessthan 10 fringes per inch. The central portion transmits the scanningbeam which strikes it directly therethrough without substantialrefraction or focusing.

The first and second end portions 122 and 124 of the optical element 20Aredirect the visible scanning beam when it strikes them and each forms adistinct cursor beam 126, 128 from the angularly extreme portion of thescanning beam, as described below with respect to FIG. 10. Each of thefirst and second portions 122 and 124 of the optical element 20A has adiffractive, segmented, sawtooth surface 125L and 125R which is tiltedslightly up and down, respectively with respect to the upper surface 119as can best be seen from FIG. 6B. The segmented surfaces 125L, 125R areformed on the outer surface of the window 20 and are protected by hardcoating the outer surface.

Alternatively, as shown in FIGS. 7A and 7B, the first and second endportions 122, 124 of the optical element may be formed from gradientsurfaces 123L, 123R or may be formed from holographic or gradient indexregions within or atop the optical element 20A. The following discussionrelates to the embodiment of FIGS. 6A and 6B; however, one skilled inthe art will understand that the discussion applies equally to thealternative embodiments employing gradient or holographic end portions.

FIG. 8 is a first diagrammatic view of the operation of the inventivereader. The discussion of the operation of the reader refers to thevisible scanning beam throughout. However, one skilled in the art willunderstand that the discussion applies equally to combination of thevisible spotter beam and an invisible scanning beam of the alternativeembodiment of FIG. 5. The portion of the scanning beam received by thecentral portion 120 is transmitted substantially unaffected. Uponstriking a target object the visible scanning beam will form a visiblescan line 131 on the target object formed by the intersection of thescan plane 24 and the target object. The portion of the scanning beamprojected through the first and second end portions 122 and 124 isredirected by each to create the pair of cursor beams 126 and 128,respectively. Because the segmented surfaces 125L and 125R are tiltedwith respect to the plane of the upper surface 119, the cursor beams 126and 128 are directed out of the scanning plane 24. Because the tiltingis in opposite directions, the cursor beams 126, 128 are made to lierespectively above and below the scan line 130. The cursor beams 126 and128 will then form a pair of visible light spots or cursor images 127,129 on a target object, on opposite sides of the scan line 130. Thisallows the user to align the scanning beam by vertically bracketing thearea which the user wishes to scan between the cursor images 127, 129.The scanning beam and the end portions 122, 124 thus form two opticalsources emitting cursor beams 126. 128 directed toward the image plane.

The inventive device not only enables a user to align the scanning beamon a target object, it also indicates a desired distance from the targetobject for optimal reading of a symbology. The performance of thescanning reader 10 is thus improved by permitting the optical componentsto be designed for a specific image-to-reader distance. As shown in FIG.10, the cursor beams 126, 128, when viewed from above, are emitted fromtwo spaced-apart locations in the reader and intersect at a focusingdistance f_(sp) (FIG. 9) which is a fixed distance from the window 20.At the focusing distance f_(sp), the first cursor beam 126 is above thescanning plane 24 and the second cursor beam 128 is below the scanningplane 24 (FIG. 9). If a target object is placed in the path of the beamsat the focusing distance f_(sp), a pair of cursor images 127, 129 willbe formed on the target object, as shown in FIGS. 9 and 13. The scanningbeam, shown as scan line 130, will be between the two cursor beam images127, 129.

At a distance d₁, less than the focusing distance f_(sp), the firstcursor beam 126 is to the left of the center line 1_(c) and the secondcursor beam 128 is to the right of the center line 1_(c). Offset cursorimages 127', 129', as shown in FIG. 9, are then formed on a targetobject positioned at the distance d₁. At a distance d₂, greater than thefocusing distance f_(sp), a pair of complementarily offset cursor images127" and 129" is formed on the target object. When the scanning reader10 is at the focusing distance f_(sp), the cursor images 127, 129 arealigned vertically. The device thus enables the user to aim and positionthe scanning beam by properly aligning the cursor images 127, 129 on thetarget object to indicate the location of the scanning beam and thedistance of the scanning reader 10 from the target object.

In addition to being redirected, the light of the scanning beam whichstrikes the first and second end portions 122, 124 can also be reshaped.In the absence of shaping, the scanning beam has an elliptical shapewhen it is in the center of its angular range of travel. It is possibleto transform the shape of the scanning beam to a substantiallycircularly shaped cursor beam when it is at the extremes of its travel.This allows light in the cursor beams to be substantially increased inbrightness by concentrating all of the optical energy into a smallercross-sectional area. Reshaping beams using segmented or gradientsurfaces or holographic elements is well known in the art and can beachieved, for example, by varying the separation of segments orproviding a curved segmented section.

In an alternative embodiment of the optical element 20 shown in FIGS.11A, 11B and 12, the optical element 20 is substantially similar to thatof the previously discussed embodiments, except that each of the secondand third portions 122 and 124 includes a pair of subportions 122U,122L, and 124U, 124L each having an upper segmented surface 125LL,125LU, and 125RL, 125RU, respectively. The upper segmented surfaces125LL and 125LU of the left portion 122 and the upper segmented surfaces125RL and 125RU of the right portion 124 are tilted down and up,respectively at equal and opposite angles to the plane of the uppersurface 119 of the central portion 120.

The subportions 122U, 124U, 122L and 124L redirect the light enteringthem when the scanning beam is at its extremes of travel. While thescanning beam is incident upon the second end portion 122, the endportion of the scanning beam is directed both above and below thecentral portion of the scanning beam by the second end portion'ssubportions because the upper segmented surfaces 125LL and 125LU aretilted oppositely with respect to each other. Light passing through theupper segmented surfaces 125LL and 125LU is thus directed below andabove the scan line 130, respectively. This forms a pair of cursor beams126U, 126L as shown in FIG. 12.

At the other extreme of travel, the emitted beam of visible light isredirected by the subportions 124U and 124L of the first end portion124. Light passing through the upper segmented surfaces 125LU and 125RUof the first end portion 124 is directed below and above the scan line130, respectively, because the upper segmented surfaces 125RL and 125RUare tilted with respect to each other. This forms two cursor beams 128Uand 128L as shown in FIG. 12.

One pair of cursor beams 126U, 128U which includes one beam from each ofthe first and second end portions 122, 124 is directed above thescanning line 130. The remaining two cursor beams 126L, 128L aredirected below the scan line 130. The upper pair of cursor beams 126L,128L and the lower pair of cursor beams 126U, 128U converge as thescanning reader 10 approaches the focusing distance f_(sp). As with theprevious embodiments, when the scanning reader 10 is held too close tothe surface on which the symbologies may be located, the cursor beams126U, 126L created when the scanning beam is at its leftmost extreme oftravel intersect the surface of the target object to the left of theline 1_(c) where the optical axis intersects the surface. Similarly,when the scanner is held too far from the surface on which thesymbologies may be located, the cursor beams 128U, 128L created when thescanning beam is at its leftmost extreme of travel intersect the surfaceof the target object to the right of the position where the optical axisintersects the surface. The cursor beams 128U, 128L created, by thesecond portion 124 will be complementarily offset, depending upon thedistance of the target object.

If the scanning reader 10 is at the distance d₁ the cursor beams 126U,126L, 128U, 128L impinge upon a target object to form two offset pairsof cursor images 127U', 127L' and 129U', 129L', as shown in FIG. 13.When the scanning reader 10 is held at the focal distance f_(sp) fromthe surface, the two pairs of cursor images 127U', 129U' and 127L',129L' coincide to form two pairs of double images 127U, 129U and 127L,129L, as shown in FIG. 13. The double images, when fully overlapped,indicate that the scanning reader is being held at the focusing distancef_(sp). The user is then able to align the scanning reader 10 to atarget object and position it to the focusing distance f_(sp) merely bymoving the scanning reader 10 to bring the two pairs of cursor images127U, 127L and 129U, 129L together.

Segmented or gradient surfaces are preferred for the upper surfaces ofsecond and third portions 122, 124 of each of the embodiments discussedabove, because unlike holographic elements, they will not be subject to"ghosting." That is, they will not cause ghost images to be producedbeyond the angular extreme of the scanned visible light beam. However,any of segmented surfaces, gradient surfaces and holographic opticalelements is within the scope of the invention and any of them can becreated by mass-production techniques.

While the detailed description above has been expressed in terms of aspecific example, those skilled in the art will appreciate that manyother elements could be used to accomplish the purpose of the disclosedinventive apparatus. Accordingly, it can be appreciated that variousmodifications of the above-described embodiments may be made withoutdeparting from the spirit and the scope or the invention. Therefore, thespirit and the scope of the present invention are to be limited only bythe following claims.

I claim:
 1. An apparatus for forming a visible scanning beam and cursorbeam for use in a scanning reader, comprising:a source for producing abeam of light, said beam being visible light; a scanning elementreceiving said beam of light and causing said beam of light to scan overa predetermined angular range in a scan plane to form a visible scanningbeam from said beam of light; and an optical element for receiving saidscanning beam from said scanning element, said optical element beingoperative to transmit said scanning beam substantially unaffected whensaid scanning beam is in a first portion of said optical element andoperative to redirect said scanning beam when said scanning beam is in asecond portion of said optical element to form a first cursor beam, thesecond portion of said optical element being positioned to receive saidscanning beam from said scanning element when scanning over a portion ofsaid angular range adjacent to the angular extreme of the angular range,said optical element further being operative to redirect said scanningbeam when said scanning beam is in a third portion of said opticalelement to form a second cursor beam spaced apart from said first cursorbeam, wherein said optical element is operative to redirect said firstand second cursor beams such that said first cursor beam is directedabove the scanning beam transmitted by the first portion and said secondcursor beam is directed below the scanning beam transmitted by the firstportion.
 2. The symbology reader of claim 1 wherein said first andsecond portions comprise segmented surface, tilted with respect to saidfirst portion of the optical element.
 3. A symbology reader,comprising:a source for producing a beam of light, said beam beingvisible light; a scanning element receiving said beam of light andcausing said beam of light to scan over a predetermined angular range ina scan plane to form a visible scanning beam; and an optical elementoperative to redirect said scanning beam when said scanning beam is in afirst portion of said optical element to form a first cursor beam,wherein said optical element is operative to redirect said scanning beamwhen said scanning beam is in a second portion of said optical elementto form a second cursor beam spaced apart from said first cursor beamand wherein said first and second portions redirect said first andsecond cursor beams above and below said scan plane respectively.
 4. Thesymbology reader of claim 3, wherein the first and second portions areselected to redirect said first and second cursor beams along respectivebeam direction to minimize the distance between the cursor beams at apredetermined focusing distance from said source producing said beam oflight.
 5. An apparatus for forming a visible spotter beam and cursorbeam for use in a scanning reader having a scanning beam, comprising:afirst source for producing a first beam of light, said first beam beingvisible light; a second source for producing a second beam of light; ascanning element receiving said first and second beams of light andcausing said first and second beams of light to scan over apredetermined angular range in a scan plane to form a visible spotterbeam from said first beam and a scanning beam substantially aligned withsaid spotter beam from said second beam; and an optical element forreceiving said spotter beam from said scanning element, said opticalelement being operative to transmit said spotter beam substantiallyunaffected when said spotter beam is in a first portion of said opticalelement and operative to redirect said spotter beam when said spotterbeam is in a second portion of said optical element to form a firstcursor beam, wherein said second portion of said optical element ispositioned to receive said spotter beam from said scanning element whenscanning over a portion of said angular range adjacent to the angularextreme of the angular range, wherein said optical element is operativeto redirect said spotter beam when said spotter beam is in a thirdportion of said optical element to form a second cursor beam spacedapart from said first cursor beam, and wherein said optical element isoperative to redirect said first and second cursor beams such that saidfirst cursor beam is directed above the scanning beam and said secondcursor beam is directed below the scanning beam.
 6. The symbology ofclaim 5 wherein said first and second portions comprise segmentedsurfaces, tilted with respect to said first portion of the opticalelement.
 7. A method for forming a visible spotter beam of light havinga cursor beam, comprising the steps of:(a) forming a first beam ofvisible light; (b) forming a second beam of light; (c) causing the firstbeam of visible light to scan over a first predetermined angular rangeto form a spotter beam; (d) causing the second beam of light to scanover a second predetermined angular range such that the second beam issubstantially coincident with the first beam during at least a portionof the second predetermined angular range to form a scanning beam; and(e) redirecting the spotter beam to form a cursor beam as the spotterbeam is scanned along a selected portion of the first predeterminedangular range by positioning a segmented surface such that the directionof the spotter beam is altered when the spotter beam is in the selectedportion of the first predetermined angular range.